1. Field of the Invention
The present invention generally relates to integrated circuit chips, and particularly relates to an integrated circuit chip for use as a RFID and to an RFID system.
2. Description of the Related Art
RFID (Radio Frequency Identification) is the system which reads/writes ID information via radio communication from/to an IC tag provided with an IC chip (integrated circuit chip) serving as a record medium for storing information. If barcodes or the like used in commercial goods management are replaced with RFIDs, for example, it is possible to eliminate the need to manually scan the barcodes or the like, thereby significantly improving the efficiency of commercial goods management.
The application of RFID in various fields in addition to its use for the purpose of identifying commercial goods is expected. In particular, RFID having a sensor function to measure the state of the environment around the IC tag can be utilized to keep a record of the manufacturing process (production process) of commercial goods and/or to keep a record of conditions during distribution.
For example, an RFID tag with a temperature sensor may be attached to perishable goods or the like to keep a record of temperature changes during distribution and/or processing of goods. This makes it possible to achieve diligent management and control of freshness and quality. With such arrangement, it is possible to properly cope with problems such as the lowering of quality of goods and to provide safe and high quality merchandise. The types of sensors that can be incorporated in RFID are not limited to a temperature sensor, but may include a three-axis sensor, a pressure sensor, an acceleration sensor, etc.
In order to implement such a sensor-equipped RFID tag, there is a need to implement a circuit having a sensor function and a measured data processing function in addition to the existing RFID function as a single chip. Incorporating the RFID function and the sensor function in a single chip requires highly sophisticated technology for combining analog circuitry and digital circuitry. There is also a need to cope with the problem of power consumption.
The performance of RFID is generally measured in terms of communication speed and communication distance. As for the communication speed, standards require a certain communication speed to be satisfied, leaving the communication distance as a factor to differentiate RFID chips from each other in terms of their performance. In order to increase communication distance, RFID chips are required to reduce power consumption inside the chip as much as possible.
IC tags are classified into an active type that operates by use of an embedded battery as a power source and a passive type that operates by use of a magnetic field or electric field supplied from an exterior as a power source without having an embedded battery. The passive type is not suited for long distance communication, but can be implemented at low price in small size owing to the absence of a battery.
A passive-type RFID chip receives a electromagnetic wave transmitted from a separate reader writer for conversion into an electric power, and stores the electric power in a capacitor provided inside the chip for use as the power supply for chip operation. The smaller the power consumption inside the chip, the smaller the electric power of the received electromagnetic wave can be, thereby achieving long distance communication. In the case of a RFID chip equipped with a sensor function, the sensor-function-purpose circuit in addition to the RFID-function-purpose circuit consumes an electric power. This makes it difficult to maintain a desired communication distance.
[Patent Document 1] Japanese Patent Application Publication No. 2004-164050
Accordingly, there is a need for an RFID IC chip and an RFID system that can allow a sensor function to operate without dropping a communication distance.